Extraction of naphthalenic hydrocarbons



Oct. 18, 1966 G. ARlcH ETAL EXTRACTION OF NAPHTHALENIC HYDROCARBONS Filed March 22, 1965 mi wi Ft 3,280,024 EXTRACTIDN F NAPHTHALENIC HYDROCARBONS Guido Aricli and Giorgio Costantinides, Trieste, Italy, as-

signors to Societe Anonyme dite: Compagnie Francaise de Railinage, Paris, France, a corporation of France Filed Mar. 22, 1963, Ser. No. 267,361 Claims priority, application France, Mar. 27, 1962, 892,409, Patent 1,326,487 14 Claims. (Cl. 208-314) This invention relates to the extraction separation of naphthalenic hydrocarbons from other hydrocarbon oomponents of mixtures containing them, such as monocyclic aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic parainic and olenic hydrocarbons, etc., and more particularly, to the efiicient and substantially complete separation of naphthalenic hydrocarbons from such mixtures by means of a liquid-to-liquid extraction utilizing a plurality of complementary solvents.

As will be understood, such mixtures of hydrocarbons are readily obtained as resulting from a variety of processes utilized in various aspects of the petroleum industry, such as thermal or catalytic cracking, catalytic reforming, the heavier products of pyrolysis of paraftns or coal tars, etc. The particular compositions of such hydrocarbon mixtures, however, may present substantial dilculty in attempting to separate therefrom naphthalenic hydrocarbons in relatively pure useable form, especially regarding the separation of naphthalenic hydrocarbons from other cyclic hydrocarbons such as, notably, the alkylbenzenes. Indeed, such well known difficulties, particularly regarding commercial scale operations, may be primarily responsible for retarding the development of the petroleum industry as an economic or fruitful commercial source of naphthalene and its derivatives.

According to this invention, however, there is provided for effecting substantially complete separation of naphthalenic hydrocarbons of desired purity from mixtures which also contain substantial proportions of aromatic, alicyclic, and aliphatic hydrocarbons by utilizing liquid phase extracting techniques with complementary polar and non-polar solvents, and under either continuous or multi-stage batch operations and conditions where the polar solvent components selectively dissolve the desired naphthalenic hydrocarbons, While the nonpolar solvent components selectively dissolve the other hydrocarbon components of the mixture; and with the various solvents and operating conditions in accordance herewith being selected and controlled particularly to enhance both the efliciency of the extracting or separating operations and the degree of selectivity of the Various solvents for the dierent hydrocarbon components or materials.

With the foregoing and additional objects in view, this invention will now be more particularly described, and other objects and advantages thereof will be apparent from the following description, the accompanying drawing, and the appended claims.

As generally illustrative of operations and techniques embodying and for practicing this invention, one may note the utilization of a 2-stage extraction arrangement, on the one hand, and, alternatively, a combined continuous double extraction operation combining the polar and non-polar -solvent extracting steps. As illustrative of the former, two successive liquid-liquid extractions are made with the polar and non-polar solvents (the selection of which is accomplished as described in more detail below) and in virtually any of a variety of conventional liquidliquid extracting tower or apparatus, although preferably operated in countercurrent manner. In the first extraction, the hydrocarbon mixture is treated with the polar solvent having a preferential or highly selective affinity United States Patent O "ice for the naphthalenic hydrocarbons in the mixture, thus giving a solvent extract phase containing in solution substantially all (or, at least, a veryi high proportion) of the desired naphthalenic hydrocarbons and, on the other hand, a residue or raffinate phase substantially free of naphthalenic hydrocarbons (or, at least, with a concentration thereof greatly diminished). In the second extraction step, the solvent extract phase is treated with a non-polar solvent immiscible with the polar solvent phase and having highly selective or preferential dissolving characteristics for hydrocarbons other than the naphthalenes, for concentrating the latter materials further in the solvent extract phase being treated, thus giving a highly concentrated extract of naphthalenic hydrocarbons in polar solvent and an immiscible phase of other hydrocarbons in a non-polar solvent. Naphthalenic hydrocarbons as a desired product are then separated from the polar solvent solution by any of a variety of appropriate and well known methods, while the non-polar phase is eliminated -or returned for recycling with the original feed or treated Iin such other manner as may be desired to recover the solvent or otherwise.

Asillustrative of the second or continuous alternative technique mentioned above, both solvent extract treatments-i.e., a pola-r solvent selectively adapted for dissolving naphthalenes and a non-polar solvent selectively adapted for dissolving other hydrocarbons in the original mixture in a phase immiscible with that of the rst or polar solvent-are combined in a double solvent treatment in any of a variety of conventional and well known liquid-liquid continuous extracting apparatus such as, for example, a countercurrent extraction column in which the polar solvent is fed in at one end, the non-polar solvent is fed vin at the other end for countercurrent circulation, and the mixture of hydrocarbons to be treated is introduced at an intermediate point, thus, a polar solvent extract phase containing substantially all of the naphthalenic hydrocarbons is withdrawn from the apparatus at one point therein, while a residue or raffinate phase of other hydrocarbons in the original mixture dissolved in the non-polar solvent is withdrawn at another point.

In the drawings:

FIG. l is a somewhat diagrammatic flow sheet embodying one form of the process of the invention; and

FIG. 2 is a flow diagram of another form of the process of this invention. y

Referring to the drawings, in which like reference characters refer to like parts throughout the several views thereof, a flow diagram embodying and for practicing the process of this invention as applied to the two-stage extraction arrangement is indicated in FIG. l. That is, a countercurrent extraction column is shown at 10 and may have an agitator shown at 11, the latter being optional and not necessary, as desired. The agitator shaft extends through the top of the extractor, and is connected to motor 12 for the rotation thereof. yThe hydrocarbon feed mixture is introduced through line 13 into the extractor, preferably near the bottom thereof, and the polar solvent having a preferential anity for the naphthalenic hydrocarbons in the feed is introduced from a source not shown through line 16 at 14, preferably near the top of the extractor. The feed and the polar solvent are subjected to countercurrent flow against each other in the extractor and a solvent extract phase containing in solution substantially all of the desired naphthalenic hydrocarbons is withdrawn from the extractor at the bottom Ithereof through line 1S. A residue or raffinate phase substantially free of naphthalenic hydrocarbons is withdrawn at 15.

The solvent extract from extractor 10 is carried through line 18 and introduced at 19 into a second extractor 20.

3 A non-polar solvent having highly selective or preferential dissolving characteristics for hydrocarbons other than naphthalene is introduced from a source not shown through line 21 into extractor 20 at 22, and preferably at a point in the extractor below the point where the solvent extract is introduced for counter ow and intermixing therewith. Water .is introduced into extractor 20 through line 23, preferably in an amount of about by weight of the solvents present for increasing the selectivity thereof.

The polar solvent containing the naphthalenic hydrocarbons is withdrawn from extractor at 29, and the non-polar Isolvent is withdrawn at 24. The non-polar solvent is carried through line to a distillation column 28 which is preferably heated by heater 27 for separating the non-polar solvents from a minor amount of nonnaphthalenic hydrocarbons. The non-polar solvent is then withdrawn from distillation column 28 through line 26 to line 21 where it is combined with new non-polar solvent for recirculation through extractor 20.

In recovering the naphthalenic hydrocarbon-s from the extract leaving extractor 20 through line 29, the extract is preferably first subjected to steam distillation in distillation column 31. Steam is introduced therein at 33, and preboiler 34 may be used as desi-red. A portion of the polar solvent is removed in distillation column 31 and is withdrawn through line 37 4to be recirculated through the system as described below.

The remaining extract containing the naphthalenic hydrocarbons is removed from distillation column 31 at 35 and flows through line 36 to Water separator 39, wherein water is introduced at 38 for aqueous extraction of the naphthalenic hydrocarbons from the polar solvent. A lighter hydrocarbon. material is preferably introduced at 40 for dilution of the naphthalenic hydrocarbons to maintain an oily layer containing the desired product which is removed from water separator 39 through line 41.

The water layer containing the polar solvent is removed through line 42-to join with line 37, wherein the polar solvent may, as desired, be recirculated through the system as by line 42 and pump 43 to line 16, after proper water removal, in known manner.

A single stage continuous extraction arrangement for carrying out the process of this invention is shown in FIG. 2, in which a ive stage countercurrent extractor is shown at 45. The hydrocarbon feed mixture from which naphthalenic hydrocarbons are to be obtained is preferably introduced into extractor 45 in the third stage from the bottom, as at 46. The polar solvent is introduced at the highest stage as at 47, and the non-polar solvent is introduced at the lowest stage as at 48 for effective countercurrent flow and intermixing with the hydrocarbon feed. Water is introduced as at 50 at a plurality of points preferably in those stages below the point wherein the feed is introduced so as to maintain the extraction by the polar solvent in a substantially anhydrous state and concentrating the water in the area of non-polar solvent extraction.

I The Apolar solvent extract containing substantially all the naphthalenic hydrocarbons is withdrawn at 53 .through line 54, wherein it is introduced into a distillation column and water separator as shown at 31 and 39 in FIG. 1 for the separation of the polar solvent and the naphthalenic hydrocarbons. A residue or raffinate phase of other hydrocarbons in the original feed dissolved in the non-polar solvent is removed at 51 from extractor 45 through line 52, where it .is carried to a distillation column for separation as shown in FIG. l at 28.

As will be apparent from the foregoing, a significant aspect of this invention, in addition to control of the particular operating and other conditions, relates to the selection of the particular complementary polar and non-polar solvents to form the two imrniscible phases desired containing naphthalenic hydrocarbons and other components of the mixture, and in a manner where, under the particular operating conditions, the solvents possess dissolving characteristics preferentially and highly selectively directed toward dissolving the particular components desired for effecting the separation `of naphthalenic hydrocarbons from those other components in the mixture which possess solubility and other characteristics so closely related to those of the desired naphthalenes that adequate commercial scale separation is tremendously' diicult. As will be understood, although a variety of important and economic tor commercial considerations are involved in the particular selection of solvent extract materials in accordance herewith, there are two primarily important characteristics or considerations relating to the distribution or partition characteristics of the particular materials desired to be separated between the polar and non-polar solvents and the selectivity characteristics or abilities of each solvent as between the two constituents or classes of constituents of the original mixture which it is desired to separate.

Purely as illustrative or as a means of simplied explanation, one may express a coefficient of distribution Ior partition of one constituent or class of constituents of the original mixture between the polar and non-polar solvents. Thus, if x and y are the concentrations in gram moles per liter of lone constituent Iof the hydrocarbon mixture repsectively in the residue or raflinite phase of nonpolar solvent and .in the solvent extract phase of the polar solvent, then the coefficient of distribution or partition K may be expressed by the relationship Similarly, an expression for the selectivity of the separation may be derived. Thus, if KN represents the distribution coecient above for the naphthalenic hydrocarbons and KA that of, for example, aromatic hydro carbons, a selectivity coefficient S may be expressed by the relationship, for the particular pair Iof solvents being considered, as

S=KN/KA As will be understood from the foregoing, it is thus possible to determine, within these parameters K and S, for each pair of solvents and for a given separation operation, the ratio or relationship of the volumes of polar solvent to non-polar solvent and as a function of the number of extraction stages; or, conversely, to determine the number of extraction stages necessary as a function yof the ratio of volumes of solvents used. Also, all things otherwise being equal, there is readily determined the particular pair of solvents to be selected for minimal solvent consumption and/ or the least number of extraction stages required for a particular completeness or eiciency of separation of naphthalenic hydrocarbons from whatever other hydrocarbon contaminants may be in the original mixture being treated.

Generally and Iin accordance herewith, the non-polar solvent utilized is preferably a hydrocarbon (or hydrocarbon cut or fraction) .of the class of aliphatic paratiinic materials having at least lthree carbon atoms (for example, propane, n-heptane, `n-dodecane, etc.), although, as will be understood, a variety of other non-polar solvent or liquid hydrocarbon materials are satisfactory for operation in accordance herewith and by the teachings set forth herein. By and large, .it has been discovered that the molecular weight of paraffinic solvents has little effect on the solvent properties thereof, at least, with those materials which'are desirably liquid at operating temperatures, so that, for example, little if any appreciable difference is noted between n-dodecane and n-heptane as appropriate non-polar solvents. Thus, the particular selection of a lnon-polar solvent material for use in accordance herewith, especially from the paran series, may depend ultimately upon such other criteria as cost, commercial availability in sufficient quantity, ease of recovery for reuse, etc.

The .selection of a particular polar solvent material i-n accordance herewith, however, is .a subs-tanti-ally more important or significant consideration, particularly in view of the fact that the polar solvent materials here are desired to combine simultaneously such disparate characteristics as high solvent properties for naphthalenic hydrocarbons, high and accutely defined selectivity for the naphthalenes as compared with .aromatic or other hydrocarbons which may be in the original mixture being treated, etc. While there `is .a variety of polar solvent materials with which satisfactory results `are achieved in accor-dance herewith, polar materials of heterocyclic nature have been found to be particularly adapted for use -in accordance herewith, Especially desirable or prefer-red are those materials having a S-member heterocyclic structure as, for example, resulting from the esteriticat-ion of a dicarboxylic acid with a l-2-diol; or :an epoxide (e.g., alkylene carbonates, ethylene carbonates, 'propylene carbonates, .and halo-substituted derivatives thereof such as chloropropylene carbonate, etc); or those resulting from the internal esteritication of .gamma hydroxyacids (eg, lactones of saturated or unsaturated gammahydroxylated acids, methylated derivatives of lactones of such .acids such .as `gamma hutyrolactone, valerolactone, crotonolac-` tone, etc.); or those resulting from the formati-on of internal am-ides from gamma .amino .acids (e.'g., lactams of .aminobutyric acids, butyrolact-ame (Z-pyrrolidone), and/or higher alkyl-substituted derivatives thereof); etc.

Although some of the aforementioned particular or illustrative solvent materials may .also possess substantial solvent properties for aromatic hydrocarbons (and, indeed, have been used for extracting and separating aromatic hydrocarbons fr-om mixtures .including 'aliphatic hydrocarbons), the different characteristics recognized .and utilized in accordance herewith-ie., .the preferential affinity and superior selectivity of such materials for naphthalenic hydrocarbons as compared to benzenic hydrooarbons--has not .generally been recognized. Especially is this true with regard .to commercial scale operations such as in .accordance herewith where such unexpected .and remarkable selectivity is utilized for an extracting separation or rectification among naphthalenic and other aromatic hydrocarbons in techniques .as embodying and for practicing .this invention, whether these tional solvents ofthe glycol and Iglycol ether family. .From comparison of these data, it will be noted that the particular solvents in accordance herewith possess good or equal selectivities at distribution coefficients higher than the other solvents. Thus, in practicing this invention, such situation produces rather notable .and important economies regarding .the volume of polar solvent utilized, etc., which considerations may, 'by comparison with the generally less expensive and more plentiful and more easily recovered non-polar solvents, .are of considerable importance in the utilization of this invention for large scale commercial installations.

As .also will be noted .among the following data, satisfactory results are Iachieved in accordance with this invention even when the various .solvents are not strictly anhydrous. Actually, it has been found that the addition or pres-ence of some proportion of water increases the selectivity of the operation but has .a concomitant tendency to decrease the solvent capacity of the materials. Preferably, in accordance herewith, the amount of water present in the solvents should be maintained at less than about 15% 'by Weight, and, even more des-irably, should -be limited .generally to within the range of no more than about 540%. Thus, as noted in the following table, data are represented to show the comparative facts obtained with Ian addition of about 110% by weight of Water to the various runs. `Such water may be introduced advantageously once into the solvent, although it is generally .advantageous to .arrange the extraction of naphthaleni-c hydrocarbons with the polar solvent in -a substantially anhydrous state .and to introduce water progressively, at least up to the above noted limits, in the sec-ond stage of extraction-ie., for .the final concentrating of the non-polar solvent extract if operating with 2-stage successive extractions-or the water is preferably introduced .at different point along the column or extraction apparatus between the base of the column and the level of introduction of the hydrocarbon charge to be treated, when operating with .the continuous double solvent treatment mentioned above.

`In the following table, the data are reported for operations at 24 C., .and the values for K are expressed as ratios between the concentration (in percent by volume) in the polar solvent phase and the concentration in the non-polar solvent phase at infinite dilution, Wit-h .the nonpolar solvent in each case bein-g normal dodecane.

OLAR SOLVENTS AT 25 C Distribution Coefficient Selectivlty Cocf., Percent Naphtha/Aromat. Polar Solvent Water in Aromat. Naphthalenic Solvent 10-0 IO-C ll-C 10-C/10C ll-C/lO-C KA KN KN' :KN/KA KN'KA Propylene Carbonate" 0 0. 32 1. 82 1. 35 5. 70 4. 22 10 0. 174 1. 10 0. 80 6. 32 4. 60

Butyrolactone 0 0. 60 2. 96 2. 00 4. 92 3. 33 10 0. 25 1. 38 0. 94 5. 52 3. 76

Diethyleueglycol O 0. 08 0. 4 5. 0 10 0.03 0.155 5. 2

Triethylcneglycol 0 0. 133 1. 00 0. 69 7. 51 5. 19 10 0. 036 0. 332 0. 210 9. 20 5. 84

Carbitol 0 0. 166 0. 788 0. 594 4. 73 3. 58 l() 0. 072 0. 404 0. 246 6. l1 3. 42

two types of hydrocarbons .are present alone or as mixed with other types of hydrocarbons.

As further illustrative or helpfully indicative of .the teachings and operations in .accordance herewith, certain data .are collected and set forth in the table below comparing :the `distribution and :selectivity coefficients of two solvents preferred in accordance herewith (pr-opylene carbonate and butyrolactone) with those of several convenof hydrocarbons in which such materials make up only a minor concentration (les-s than, perhaps, `30% of the total polycyclic hydrocarbons) :and incl-udi-ng paraffini-c, olefinic, and alkylbenzene hydrocarbons, by treating the mixture, at operating temperatures ge-nerally in the neighborhood Aof ambient temperature, -with from 0.3 to 3 volumes of polar solvent per volume of hydrocarbon mixture charge to be treated and, preferably, utilizing as the polar solvent range 0.7 to 1.2 volumes i-n the case :where the 2-stage extraction technique -in laccordance herewith is utilized. Under the operations with the continuous tor double solvent extraction technique described above, satisfactory resul-ts `are achieved with the proportions of polar solvent being within the range of 0.5 to 3.5 volumes broadly and, preferably, from 1 to 1.8 volumes -of solvent per volume of mixture being treated. From the data expressed in the table, for example, one can note that utilization -of known glycol-type solvents for naphthalenic hydrocarbons requires, under substantially the :same or comparable conditions, at least two t-o three times more solvent volurne.

Regarding the proportion of non-polar solvent, particularly of the type of parainic hydrocarbons, to be utilized with a polar solvent as indicated above satisfactory results in accordance herewith are achieved with a ratio by volume of polar solvent to parainic non-polar solvent of within the range of about 0.3 to 2.4, and preferably between 0.7 and 1.2 volumes of polar solvent per volume of non-polar solvent in the case of a 2-stage successive extraction; whereas, with the continuous or double solvent technique, these ranges are satisfactorily from 1.5 to 7.0 generally and, preferably, 2.5 to 4.0. As will be understood from the foregoing, of course, if the original mixture to be treated is substantially richer in naphthalenic hydrocarbons, or concomitantly leaner in aromatic or benzene hydrocarbons, or if there is no need to obtain complete extraction of naphthalenes, then the quantity of polar solvent utilized, as related to the original hydrocarbon mixture or charge, may satisfactorily be reduced in substantial proportions, even as much as 60 t0 70% of the values noted above.

Although operations at substantially room temperature or ambient temperature are preferred, the techniques in accordance herewith may be satisfactorily performed at elevated temperatures up to as much as 125 C., although employing such elevated temperatures may not particularly be preferred in the sense that the degree or criticality of selectivity tends to diminish at elevated temperatures.

As will be understood, the final separation of extracted naphthalenic hydrocarbons from the polar solvent extract phase and the recovery of the polar solvent for reuse is satisfactorily accomplished by any of the variety of known or conventional techniques such as, for example, distillation, aqueous extraction, etc. Recovery of the nonpolar solvent, especially with paraflinic types of materials, is also readily accomplished, although preferably by distillation. Generally, it may be preferred to recover the polar solvent by aqueous extraction, perhaps after a preliminary distillation step. The ultimate dehydration of solvent is then accomplished by conventional means. Of course, recovery or separation of the polar solvent by water extraction may require the dilution of naphthalenic hydrocarbons with a lighter hydrocarbon material to facilitate the separation of a oily layer or phase containing the desired naphthalenic product from an aqueous phase containing the polar solvent for reuse. That is, the naphthalenic hydrocarbon extracts may have, actually, a density so close to that of water that a truly eflicient or rapid decantation on commercial scale may be relatively difficult, and there may also be a risk of some crystallization after solvent removal. Nevertheless, ultimate recovery of the desired naphthalenic product and of polar solvent for reuse is readily accomplished. Also, many of the paraflinic type of non-polar solvents are g sufficiently soluble in the naphthalenic extract to avoid the necessity of subsequent dilution in the recovery step, all according to well understood knowledge.

Merely as further illustrative of techniques and arrangements embodying and for practicing this invention, one may note the following examples:

Example I Naphthalenic hydrocarbons were separated from a hydrocarbon mixture having a composition, by weight, of 60% saturated hydrocarbons (normal dodecane), 20% alkylbenzenes (durene), 5% naphthalene, and 15% 1- rnethylnaphthalene. For this example, satisfactorily effected under conditions of commercial scale or industrial operation, propylene carbonate was utilized as the polar solvent and normal heptane as the nonpolar solvent.

Operating at temperatures of about 20 C., 80 gms. of the hydrocarbon mixture (about 100 cc.) were vigorously agitated with 50 cc, of propylene carbonate, and a first decantation produced a lower layer or extract rich in polar solvent. The upper layer of the decanted material or raffinate was treated anew with 50 cc. of propylene carbonate, from which second treatment was separated a second extract layer rich in polar solvent, which was added to that of the first extraction and washed with four successive portions of 25 cc. normal heptane. The thus treated and washed phase was diluted one liter of water, from which 5.68 gms. of oily supernatant fluid was separated having a composition of, approximately by weight, 6.8% alkylbenzenes, 28.4% naphthalene, and 64.8% l-methylnaphthalene, and being substantially free of saturated hydrocarbons such as the originally present normal dodecane. The concentration of the naphthalenic hydrocarbons (which totaled about 25% in the original mixture) increased to 93.2% of the final extract, with a recovery of 33.1% of the naphthalenic material actually present in the original mixture.

Example Il A comparative repetition ofthe run described above was made, but replacing the propylene carbonate by butyrolactone as the polar solvent. Thus, gms. of the same hydrocarbon mixture was treated with two successive portions of 32.5 cc. anhydrous butyrolactone, at ambient temperatures of about 20 C. The extract phases were combined and washed with four successive portions of 25 cc. of n-heptane, and the fraction rich in polar solvent finally obtained had then added thereto 300 cc. of water. From this there was separated an oily phase of about 7.86 gms. and in which the various hydrocarbons were distributed as, in proportions by weight, 13.4% alkylbenzenes (durene), 25.8% naphthalene, and 60.7% 1rnethylnaph thalene, with substantially no discernible saturated hydrocarbons such as n-dodecane. The composition of naphthalenic hydrocarbons (originally 20% in the charge) had increased 86.5% in the final extract, and there was thus recovered from the process 42.5% of the originally present naphthalenic materials as the final product.

Example III In this instance there was treated a fraction or mixture of hydrocarbons in a 20W-240 C. cut of catalytic gas oil material preliminarily desulphurized and having the approximate composition by volume of 31.6% saturated hydrocarbons, 42.1% aromatic hydrocarbons, 5.2% naphthalene, 21.1% methylnaphthalene, and traces of thionaphthene. This material was treated in accordance with the double solvent arrangement in connection herewith and utilizing a 5-stage extraction tower, and was introduced into such tower at the third stage from the bottom, while also feeding into the top of the tower butyrolactone as the polar solvent (at a rate of about two volumes of solvent per volume of charge) and at the base of the tower a parafiinic non-polar solvent (n-dodecane) at the same rate of two volumes solvent per volume of charge. The apparatus was operated at about 25 C.

After elimination and re-covery of the solvents from the withdrawn materials, there were recovered, for each 100 volumes of mixture charged, 25 volumes of extract phase and 75 volumes of rainate. In volume percent, the extract phase contained approximately 1.2% saturated hydrocarbons, 21.1% aromatic hydrocarbons, 16.0% naphthalene, and 61.7% methylnaphthalene; while the railinate phase contained 41.7% saturated hydrocarbons, 49.2% aromatic hydrocarbons, 1.7% naphthalene, and 7.8% methylnaphthalene. Thus, 74% of the total of the naphthalenic hydrocarbons in the original charge were recovered at a concentration of 77.7% by volume in the extract.

Example IV For illustrative comparison, the operation of Example I was repeated but utilizing chloropropylene carbonate for the propylene carbonate used originally as the polar solvent. Thus, 80 gms. of the same hydrocarbon mixture was treated with two successive portions of 50 cc. of anhydrous chloropropylene carbonate at ordinary temperature of about C. The two extracts were combined and then washed with four successive portions of cc. of n-heptane, and the finally obtained fraction rich in solvent was added to 1,500 cc. water. An oily phase was then separated weighing about 6.55 gms., in which the various hydrocarbon components were present, weight percent approximately as 9.85% alkylbenzenes (durene), 26.4% naphthalene, 63.8% l-methylnaphthalene, and substantially none of the original saturated hydrocarbons (n-dodecane). Thus, the concentration of naphthalenic hydrocarbons (originally 20% of the charge) was raised to 90.2% in the nal extract, recovering 36.9% of the original naphthalenic hydrocarbons present.

Example V A similar run was made utilizing valerolactone as the polar solvent. Thus, 80 gms. of the same hydrocarbon mixture was treated with two successive portions of cc. of anhydrous valerolactone at a temperature of about 20 C. The two extracts were combined and washed with four successive portions of 25 cc. of n-heptane, and the fraction rich in solvent 'finally obtained was added to 300 cc. water. From this mixture was separated an oil phase of about 7.70 gms., in which the various hydrocarbons appeared, by weight, as 8.8% alkylbenzene, 25.0% naphthalene, 66.2% l-methylnaphthalene, and substantially no dodecane. The concentration of the naphthalenic hydrocarbons (originally 20% of the charge) was raised to 91.2% in the nal extract, and there was thus recovered 43.8 of the originally present naphthalenic materials.

Example VI The above runs were then again repeated utilizing methyl-2-pyrrolidone as the polar solvent. Thus, 80 gms. -of the same hydrocarbon mixture was treated with two successive portions of 35 cc. of anhydrous methyl-Z-pyrrolidone at temperatures of about 20 C. The two extracts were combined and washed with four successive portions of 25 cc. n-heptane, and the fraction rich in solvent was added to 500 cc. water. From this mixture was separated an oily phase of 6.72 gms., in which the various hydrocarbons appeared, by weight, as 18.0% alkylbenzene, 21.8% naphthalene, 60.2% l-methylnaphthalene, and substantially no saturated hydrocarbons. The concentration of naphthalenic hydrocarbons (originally 20% of the charge) was raised to about 82.0% in the final extract, thus recovering 34.4% of the originally present naphthalenic hydrocarbons.

As will be apparent from the foregoing, there are provided in accordance herewith techniques for the solvent extraction or separation of naphthalenic hydrocarbons from mixtures thereof with other hydrocarbons and under circumstances of enhanced efficiency and selectivity, even when the other hydrocarbons in the mixtures are closely related in physical and other properties and/or solubility characteristics to the desired final product. Similarly, both batch-type and continuous or double solvent techniques are provided utilizing treatment with complementary polar and non-polar solvents for the separation and concentration of the desired naphthalenic materials, and under circumstances where the solvents are readily recovered for reuse, while also providing for the utilization of particular solvent materials under circumstances where high ainity and selectivity for the various components to be separated may be achieved for enhanced results hitherto unknown, especially with the economic commercial scale utilization of petroleum materials as sources of naphthalenic hydrocarbons in a relatively pure state.

While the methods and compositions described herein form preferred embodiments of this invention, this invention is not limited to these precise methods and compositions, and modifications may be made therein without departing from the scope of this invention which is defined in the appended claims.

What is claimed is:

1. In a process for extracting naphthalenic hydrocarbons from mixtures thereof containing other aromatic and aliphatic hydrocarbon components having closely related physical properties and solubility characteristics, the steps which comprise treating said mixture in liquid phase and in countercurrent manner with a liquid polar extracting solvent im-miscible therewith and having preferential solvent ainity and selectivity for said naphthalenic hydrocarbons and selected from the group consisting of live-member heterocyclic esters of dicarboxylic acids with di-ols, epoxides, halo-substituted derivatives thereof, internal esters of gamma hydroxyacids, methylated derivatives thereof, internal amides of gamma amino acids, higher alkyl-substituted derivatives thereof, and mixtures thereof, forming a separate liquid extract phase rich in said solvent with said naphthalenic hydrocarbons dissolved therein and a liquid raffinate phase rich in said other hydrocarbon components of said original mixture, treating said extract phase in liquid phase and in countercurrent manner with a liquid non-polar aliphatic hydrocarbon extracting solvent immiscible with said polar solvent and having preferential solvent anity and selectivity for said other hydrocarbon components of said mixture forming a separate liquid extract phase rich in said -other components separated from said polar solvent solution, separating said polar solvent solutions of said naphthalenic hydrocarbons, and recovering said naphthalenic hydrocarbons therefrom.

2. A process as recited in claim 1 in which said extraction steps are conducted at operating temperatures within the range of from ambient temperature up to about C.

3. A process as recited in claim 1 in which said polar solvent is substantially anhydrous.

4. A process as recited in claim 1 in which said polar solvent is utilized within the range of about 0.3 to 3.0 volumes of solvent per volume of said hydrocarbon mixture being treated.

5. A process as recited in claim 1 in which said polar' solvent is utilized within the range of about 0.7 to 1.2 volumes of solvent per volume of said hydrocarbon mixture being treated.

6. A process as recited in claim 1 in which the volume ratio of said polar solvent to said non-polar solvent is within the range of about 0.3 to 2.4.

7. A process as recited in claim 1 in which the volume ratio of said polar solvent to said non-polar solvent is within the range of about 0.7 to 1.2.

8. In a continuous process for extracting naphthalenic hydrocarbons from mixtures thereof containing other aromatic and aliphatic hydrocarbon components having closely related physical properties and solubility characteristics, the steps which comprise establishing a countercurrent double solvent treating extraction zone, introducing into one end of said zone a liquid polar extracting solvent immiscible with said mixture and having preferential solvent aflinity and selectivity for said naphthalenic hydrocarbons and selected from the group consisting of -member heterocyclic esters of dicarboxylic acids with diols, epoxides, halo-substituted derivatives thereof, internal esters of gamma hydroxyacids, methylated derivatives thereof, internal amides of gamma amino acids, higher alkyl-substituted derivatives thereof, and mixtures thereof, introducing into the opposite end of said zone for counter-current flow -therethrough a liquid non-polar aliphatic hydrocarbon extracting solvent immiscible with said solvent and having preferential solvent atlinity and selectivity for said other hydrocarbon components of said mixture, introducing said mixture of naphthalenic and other hydrocarbon components into said treating and extracting zone intermediate the points at which said polar and non-polar solvents are introduced, effecting in said zone liquid phase extraction and dissolving of said naphthalenic hydrocarbons by said polar solvent forming a distinct liquid phase of naphthalenic hydrocarbons dissolved in said polar solvent, increasing the concentration of naphthalenic hydrocarbons in said polar solvent solution in said zone by contact therein with said non-polar solvent effecting liquid phase extraction and solution thereby of said other hydrocarbon components from said polar solvent solution, withdrawing said polar solvent solution of said concentrated naphthalenic hydrocarbons from said treatment zone, and separating said naphthalenic hydrocarbons from said solution.

9. A process as recited in claim 8 in which said polar solvent is utilized within the range of about 0.5 to 3.5 volumes of solvent per volume of said hydrocarbon mixture being treated.

10. A process as recited in claim 8 in which said polar solvent is utilized within the range of about 1.0 to 1.8 volumes of solvent per volume of said hydrocarbon mixture being treated.

11. A process as recited in claim 8 in which the volume ratio of said polar solvent to said non-polar solvent is within the range of about 1.5 to '7.0.

12. A process as recited in claim 8 in which the volurne ratio of said polar solvent to said non-polar solvent is within the range of about 2.5 to 4.0.

13. A process as recited in claim 8 in which sai-d polar soflvent contains less than about 15% water.

14. A process as recited in claim 8 in which said extraction steps are conducted at operating temperatures within the range of from ambient temperature up to about C.

References Cited by the Examiner UNITED STATES PATENTS 2,095,972 10/ 1937 Faragher 208-317 2,319,813 5/1943 Grosse et al. 208-337 2,803,685 8/1957 Poffenberger et al. 208-317 2,812,372 11/1957 Walsh et al 260-674 2,943,122 6/1960 Templeman et al. 208-326 2,963,427 12/1960 Nevitt 208-326 2,963,429 12/1960 Morin et al 260-674 3,051,650 8/1962 Pfennig 260-674 3,210,259- 10/1965 Cornell et al. 208-326 FOREIGN PATENTS 459,595 1/1937 Great Britain.

DELBERT E. GANTZ, Primary Examiner. ALPHONSO D. SULLIVAN, H. LEVINE,

Assistant Examiners. 

1. IN A PROCESS FOR EXTRACTING NAPHTHALEINE HYDROCARBONS FROM MIXTURES THEREOF CONTAINING OTHER AROMATIC AND ALIPHATIC HYDROCARBON COMPONENTS HAVING CLOSELY RELATED PHYSICAL PROPERTIES AND SOLUBILITY CHARACTERISTICS, THE STEPS WHICH COMPRISES TREATING SAID MIXTURE IN LIQUID PHASE AND A COUNTERCURRENT MANNER WITH A LIQUID POLAR EXTRACTING SOLVENT IMMISCIBLE THEREWITH AND HAVING PREFERENTIAL SOLVENT AFFINITY AND SELECTIVELY FOR SAID NAPHTHALENIC HYDROCARBONS AND SELECTED FROM THE GROUP CONSISTING OF FIVE-MEMBER HETEROCYCLIC ESTERS OF DICARBOXYLIC ACIDS WITH DIOLS, EPOXIDES, HALO-SUBSTITUTED DERIVATIVES THEREOF, INTERNAL ESTERS OF GAMMA HYDROXYACID, METHYLATED DERIVATIVES THEREOF, INTERNAL AMIDES OF GAMMA AMINO ACIDS, HIGHER ALKYL-SUBSTITUTED DERIVATIVES THEREOF, AND MIXTURES THEREOF, FORMING A SEPARATE LIQUID EXTRACT PHASE RICH IN SAID SOLVENT WITH SAID NAPHTHALENIC HYDROCARBONS DISSOLVED THEREIN AND A LIQUID RAFFINATE PHASE RICH IN SAID OTHER HYDROCARBON COMPONENTS OF SAID ORIGINAL MIXTURES TREATING SAID EXTRACT PHASE IN LIQUID PHASE AND IN COUNTERCURRENT MANNER WITH A LIQUID NON-POLAR ALIPHATIC HYDROCARBON EXTRACTING SOLVENT IMMISCIBLE WITH SAID POLAR SOLVENT AND HAVING PREFERENTIAL SOLVENT AFFINITY AND SELECTIVITY FOR SAID OTHER HYDROCARBON COMPONENTS OF SAID MIXTURE FORMING A SEPARATE LIQUID EXTRACT PHASE RICH IN SAID OTHER COMPONENTS SEPARATED FROM SAID POLAR SOLVENT SOLUTION, SEPARATING SAID POLAR SOLVENT SOLUTIONS OF SAID NAPHTHALENIC HYDROCARBONS, AND RECOVERING SAID NAPHTHALENIC HYDROCARBONS THEREFROM. 